The invention relates to scanning systems for document copying machines. The invention has particular application where an image of an original is projected onto a moving photosensitive surface.
A copying machine such as that described in British Patent Specification No. 995,413 uses an optical system comprising two fixed mirrors with a lens between the mirrors, the stationary original being illuminated by lamps on a movable lamp carriage, and light from the original being screened from the projection system except for a small slit between the lamps. British Patent Specification No. 1,122,622 describes a document copying machine in which the whole of the stationary original is illuminated during exposure, and scanning is achieved by oscillating one of the mirrors of the projection system about an axis in its plane. It has been proposed, for example in U.S. Pat. Specification No. 3,642,366 to have a more compact image projection system in which two mirrors are moved in different directions at speeds relating to the speed of movement of the photosensitive surface.
With a two mirror system an illuminator is mounted for traveling with one of the mirrors and this introduces additional mechanical inertia of the illuminator itself and its mountings. Further, the movements of scanning can be abrupt and subject to severe decelerations tending to reduce the life of the lamp.
It is an object of the present invention to provide an improved scanning system.